(Dow Jones) -- U.S. farm incomes are expected to fall 13.8% this year to the lowest level in four years, the U.S. Department of Agriculture said on Tuesday, as expectations of a second straight bumper harvest push down prices for key crops.

Federal forecasters projected net farm income would slide to $113.2 billion this year from an estimated $131.3 billion in 2013, which was the highest level since 1973 on an inflation-adjusted basis.

The latest projected decline is significantly narrower than the 27% drop in 2014 net farm income that the USDA forecast in February. The change is due largely ...